Chapter 11: Problem 3
Solve each equation. $$\log (x+100)=3$$
Short Answer
Expert verified
x = 900
Step by step solution
01
Understand the problem
We need to solve the equation involving a logarithm: \(\log{(x+100)} = 3\). Our goal is to find the value of \(x\).
02
Remove the logarithm
To remove the logarithm, rewrite the equation in exponential form. Recall that \( \log_b{a} = c \) can be rewritten as \( b^c = a \). Here, the base is 10 (since it’s the common logarithm): \( 10^3 = x + 100 \).
03
Simplify the exponential equation
Calculate \( 10^3 \): \(10^3 = 1000\). So, the equation becomes \( 1000 = x + 100 \).
04
Solve for \( x \)
Subtract 100 from both sides of the equation: \( 1000 - 100 = x \). Simplify to find \( x = 900 \).
05
Verify the solution
Substitute \( x = 900 \) back into the original equation to verify: \( \log{(900 + 100)} = \log{1000} = 3 \). This confirms our solution is correct.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Exponential Form
When solving logarithmic equations, converting to exponential form is a critical step. Understanding the relationship between logarithms and exponents is essential. To go from logarithmic to exponential form, remember the rule: \( \log_b{a} = c \) means \( b^c = a \). This conversion helps you eliminate the logarithm and deal directly with the numbers.
For the equation \( \log{(x + 100)} = 3 \), we use the common logarithm base, which is 10. So, \( \log{(x + 100)} = 3 \) translates to \( 10^3 = x + 100 \). This simplifies the problem significantly.
When you rewrite logarithmic equations in their exponential form:
For the equation \( \log{(x + 100)} = 3 \), we use the common logarithm base, which is 10. So, \( \log{(x + 100)} = 3 \) translates to \( 10^3 = x + 100 \). This simplifies the problem significantly.
When you rewrite logarithmic equations in their exponential form:
- You make it easier to isolate the variable.
- It becomes straightforward to solve using arithmetic operations.
Common Logarithm
The common logarithm is a logarithm with base 10. It is represented as \( \log{x} \) without a base. It is commonly used in scientific calculations and standard mathematical problems.
In the equation \( \log{(x + 100)} = 3 \), the absence of a base means we are dealing with a common logarithm, or base 10. This makes calculations simpler because the base is consistent and well-understood.
The properties of common logarithms include:
In the equation \( \log{(x + 100)} = 3 \), the absence of a base means we are dealing with a common logarithm, or base 10. This makes calculations simpler because the base is consistent and well-understood.
The properties of common logarithms include:
- Easy conversion to exponential form since \( \log_b{x} = y \) converts to \( 10^y = x \).
- Frequently used in practical applications, from measuring the intensity of earthquakes to calculating compound interest rates.
Solving Equations
Solving logarithmic equations involves a series of steps that simplify the problem. Let's break down the process discussed in the solution:
First, write down the equation: \( \log{(x + 100)} = 3 \). By converting this to exponential form, you get \( 10^3 = x + 100 \). This removes the logarithm and simplifies the equation.
Next, you calculate \( 10^3 = 1000 \), leaving you with \( 1000 = x + 100 \).
Then, solve for \( x \) by isolating it on one side. Subtract 100 from both sides of the equation: \( 1000 - 100 = x \). You then get \( x = 900 \).
Finally, verify the solution by substituting \( x \) back into the original equation: \( \log{(900 + 100)} = \log{1000} = 3 \). This confirms the correctness of \( x \).
Following these steps helps you tackle logarithmic equations systematically:
First, write down the equation: \( \log{(x + 100)} = 3 \). By converting this to exponential form, you get \( 10^3 = x + 100 \). This removes the logarithm and simplifies the equation.
Next, you calculate \( 10^3 = 1000 \), leaving you with \( 1000 = x + 100 \).
Then, solve for \( x \) by isolating it on one side. Subtract 100 from both sides of the equation: \( 1000 - 100 = x \). You then get \( x = 900 \).
Finally, verify the solution by substituting \( x \) back into the original equation: \( \log{(900 + 100)} = \log{1000} = 3 \). This confirms the correctness of \( x \).
Following these steps helps you tackle logarithmic equations systematically:
- Convert to exponential form.
- Simplify and solve for the variable.
- Verify the solution to ensure accuracy.